Various designs of tool closing systems for blow molding machines are known. A design used by various machine manufacturers accomplishes a symmetrical force introduction via a drive arranged underneath the mold and a symmetrical lever mechanism. In practice, however, this bottom type drive is objectionable in various production variants. Moreover, due to the lever mechanism used, the mechanical structure is relatively complicated and an increase in the opening stroke is only possible with great difficulty.
A further common design is the so-called 3-plate system. The drive is arranged in this system behind the third plate (so-called crosshead). The synchronous movement of the two mold halves towards a joint mold parting plane is normally ensured via rack or lever synchronization. Advantages of this system are the relatively easy compensation of different mold thicknesses and strokes and the ease of access to the mold from below for cooling, waste belts and bottom-type blow station. Of disadvantage are the deformations in the area of the guides of the closing plate, the deformations being particularly caused by the bending moment produced due to the system on the front closing plate. Comparatively great efforts are required for compensating for such deformations. Especially in the case of large mold projections, problems arise with respect to the force distribution, which problems cannot easily be solved by the structural design of the whole force system.
Further known closing unit systems also work with a drive located at the “rear” and try to prevent the introduction of any bending into the guide system of the mold clamping plate by way of very complexly designed lever mechanisms or intermediate plates.